The political and cultural impact of the Black Death, which is usually seen as beginning in the period 1347-1353, on European life was immense. At least a hundred million people were killed (and possibly more than twice that by some estimates), reshaping the economy of feudalism and influencing the wars and politics that followed for at least the next four centuries, as plague outbreaks struck cities and villages over and over again. The bacteria responsible, Yersinia pestis, has long been believed to have originated in China, and to have been carried from east to west in fleas living on black rats that migrated with the merchants moving along the Silk Road, first by camel across central Asian steppes and deserts, and then across the Black Sea and Mediterranean by ship to major trading ports like Venice.

This distributional jigsaw may be missing some pieces, however - a new study by Norwegian and Swiss bioscientists and climatologists instead points the finger at some different rodents as bearing some of the responsibility for spreading plague: grey marmots, long-tailed squirrels, camels and Mongolian gerbils.

In the paper, published in the Proceedings of the National Academy of Sciences, the authors looked at 4,119 records of historical plague outbreaks across Europe, and cross-referenced them with 15 climate records derived from analysing tree rings within the same regions as the outbreaks. They were testing the hypothesis that the plague, once it arrived in Europe, dug itself in by living among rat populations (or "rat reservoirs" as the authors call them), which then experienced regular population swellings and shrinkings as the climate adjusted to become more or less rat-friendly over the centuries. They expected to see that plague outbreaks correlated neatly with warmer, drier summers, and that periods with fewer outbreaks were wetter and colder - yet it didn't quite work.

Most of the outbreaks in the records could be traced to other outbreaks nearby, but there were a select few - 16 in total, all in port cities like London, Lisbon and Hamburg - which had no connection with other outbreaks nearby, and where brand new imports of Y pestis via trading ships must have been responsible.

This, in itself, isn't too remarkable, but the researchers did notice a strong correlation between the climate records of east Asia and these 16 outlier European plague outbreaks. For each of them, certain climate conditions in east Asia would, 15 years later, be followed by a large outbreak. Something was linking the two sides of the Eurasian continent, and the researchers see a number of different rodents as responsible.

Consistently, a warming climate followed by a sudden cooling seemed to kickstart the transmission of plague bacteria across the Silk Road. The researchers theorise that warmer summer made it easier for fleas to find hosts to live and feed on - but the crash in temperature kills those same hosts, meaning fleas jump to new species, including humans. The model they propose has this happening over the first couple of years after the climate event; then, as those fleas move through the human population, they hitch onto humans on the edge of the Silk Road trading networks of central Asia.

From there, the plague moved slowly over a decade or so along trading routes, surviving in the large populations of rodents that live in those areas. Once the migration hit the eastern edge of the Black Sea, the journey was then sped up thanks to the speed of ships - within two or three more years, the plague will have successfully travelled from one side of the world to the other, to infect those living in European cities. "This association strongly suggests that the bacterium was continuously reimported into Europe during the second plague pandemic," writes lead author Boris Schmid of the University of Oslo, "and offers an alternative explanation to putative European rodent reservoirs for how the disease could have persisted in Europe for so long."

This doesn't get the black rat (Rattus rattus) off the hook - it's still the key vector for plague transmission once the bacteria arrived in Europe with each new wave. But it does mean that other members of the rodent family lose some of their ability to act all cute and innocent.

Marcus Hutchins: What we know so far about the arrest of the hero hacker

In May, Marcus Hutchins - who goes by the online name Malware Tech - became a national hero after "accidentally" discovering a way to stop the WannaCry virus that had paralysed parts of the NHS.

Now, the 23-year-old darling of cyber security is facing charges of cyber crime following a bizarre turn of events that have left many baffled. So what do we know about his indictment?

Arrest

Hutchins, from Ilfracombe in Devon, was reportedly arrested by the FBI in Las Vegas on Wednesday before travelling back from cyber security conferences Black Hat and Def Con.

He is now due to appear in court in Las Vegas later today after being accused of involvement with a piece of malware used to access people's bank accounts.

"Marcus Hutchins... a citizen and resident of the United Kingdom, was arrested in the United States on 2 August, 2017, in Las Vegas, Nevada, after a grand jury in the Eastern District of Wisconsin returned a six-count indictment against Hutchins for his role in creating and distributing the Kronos banking Trojan," said the US Department of Justice.

"The charges against Hutchins, and for which he was arrested, relate to alleged conduct that occurred between in or around July 2014 and July 2015."

His court appearance comes after he was arraigned in Las Vegas yesterday. He made no statement beyond a series of one-word answers to basic questions from the judge, the Guardian reports. A public defender said Hutchins had no criminal history and had previously cooperated with federal authorities.

The malware

Kronos, a so-called Trojan, is a kind of malware that disguises itself as legitimate software while harvesting unsuspecting victims' online banking login details and other financial data.

It emerged in July 2014 on a Russian underground forum, where it was advertised for $7,000 (£5,330), a relatively high figure at the time, according to the BBC.

Shortly after it made the news, a video demonstrating the malware was posted to YouTube allegedly by Hutchins' co-defendant, who has not been named. Hutchins later tweeted: "Anyone got a kronos sample."

His mum, Janet Hutchins, told the Press Association it is "hugely unlikely" he was involved because he spent "enormous amounts of time" fighting attacks.

Research?

Meanwhile Ryan Kalember, a security researcher from Proofpoint, told the Guardian that the actions of researchers investigating malware may sometimes look criminal.

“This could very easily be the FBI mistaking legitimate research activity with being in control of Kronos infrastructure," said Kalember. "Lots of researchers like to log in to crimeware tools and interfaces and play around.”

The indictment alleges that Hutchins created and sold Kronos on internet forums including the AlphaBay dark web market, which was shut down last month.

"Sometimes you have to at least pretend to be selling something interesting to get people to trust you,” added Kalember. “It’s not an uncommon thing for researchers to do and I don’t know if the FBI could tell the difference.”

It's a sentiment echoed by US cyber-attorney Tor Ekeland, who told Radio 4's Today Programme: "I can think of a number of examples of legitimate software that would potentially be a felony under this theory of prosecution."

Hutchins could face 40 years in jail if found guilty, Ekelend said, but he added that no victims had been named.

This article also appears on NS Tech, a new division of the New Statesman focusing on the intersection of technology and politics.